DE102006041469B3 - Coating anti-reflection layer containing silicon dioxide on a borosilicate glass body comprises wetting the body containing e.g. silicon dioxide with a coating solution containing e.g. hydrochloric acid, followed by drying and annealing - Google Patents

Abstract

Procedure for coating a liable- and washable anti-reflection layer containing porous silicon dioxide, on a boro-silicate glass body, comprises wetting the body containing silicon dioxide (70-75 wt.%), boron trioxide (8-11 wt.%), aluminum trioxide (5-9 wt.%), alkaline oxide (7-12 wt.%) and alkaline earth oxide (0-10 wt.%), coating with a solution containing hydrochloric acid (1-6 wt.%), silicon dioxide-sol (solid material content) (0.5-7 wt.%), water (0.5-5 wt.%) and easily volatile and water-soluble organic solvent (85-98 wt.%), and drying and annealing the coating. An independent claim is included for a coating solution for the production of anti-reflection layers on boro-silicate glass.

Description

The invention relates to a process for producing an adhesive and smudge-resistant, porous SiO ₂ -containing antireflection coating on a borosilicate glass body and coating solution suitable therefor.

DE 100 51 724 A1 describes a thermally toughened soda-lime glass provided with a porous SiO ₂ antireflective layer, in which the glass is coated with a solution of an aqueous SiO ₂ sol and a surfactant mixture, the coated glass dried to temperatures of at least Heated to 600 ° C and quenched by blowing with air. DE 100 51 725 A1 describes a similar coating solution for the same purpose wherein the surfactant mixture consists of 10-30% by weight of anionic surfactants, 5-15% by weight of nonionic surfactants and less than 5% by weight of amphoteric surfactants.

Out DE 101 46 687 C1 For example, a glass with a porous SiO ₂ antireflective layer is known in which the surface coating has a first particle fraction with a particle size of 3 to 13 nm and a second particle fraction with a particle size of 20 to 50 nm. The glass can be like at DE 100 51 724 A1 heated to at least 600 ° C and biased by blowing cold air.

DE 100 52 075 A1 describes a method for producing porous layers and their use in microelectronics, in which a suspension of silicalite-1 (zeolite) with a SiO ₂ sol as binder is spin-coated on a substrate and baked at about 420 ° C. ,

According to EP 1 167 313 A1 For example, an antireflective glass article such as an automobile windshield, window glass, and the like is produced by baking SiO ₂ particles having a size of 40-1000 nm in the presence of SiO ₂ gel on the disc. The SiO ₂ gel serves as a binder and preferably completely covers the surface of the SiO ₂ particles.

All The above publications are concerned with the generation of layers on soda-lime glass.

It is known that porous SiO ₂ layers adhere poorly to borosilicate glass bodies. This applies in particular to layers which have been produced using a SiO ₂ sol.

To improve the adhesion, it has already been proposed to add tetraethyl orthosilicate to the sol, the decomposition products of which adhere the SiO ₂ particles to one another and to the substrate ( US 2,601,123 ). However, these solutions are complicated to manufacture and relatively expensive.

Out EP 0 897 898 B1 For example, a method using a purely aqueous coating solution containing SiO ₂ sols and surfactants is known. In this method, a pretreatment of the substrate to be coated with acetone, ethanol and water, a strong alkaline cleaning solution (1nNaOH) or commercially available cleaning baths is mandatory, where appropriate, the cleaning effect must be enhanced by the application of ultrasound. In particular, the purification steps (see Example 1) make this process consuming.

Out EP 1 342 702 A1 respectively. US 6,998,177 B2 is a procedurally favorable method is known in which an alcoholic, salper tersäure-stabilized suspension of a SiO ₂ sol is used. The known poor adhesion and wipe resistance of the formed SiO ₂ particle layer is avoided by adding H ₃ PO _{4 to} the coating liquid. Although the adhesion and wipe resistance of the antireflection coating thus produced is very good, it has been found that such layers age in the course of a few weeks, which is manifested by the fact that the originally deep blue antireflection layers fade and cloud, so that the desired high Transmittance for incident light and wipe resistance go back. This fading can be reversed by washing with water. It can be avoided if the glass bodies provided with the antireflection coatings are still washed with water in the factory after their production, thus eliminating the problem of aging in practice. However, this washing step means an undesirable additional effort.

The The object of the invention is a coating method and a coating solution find that similar easy to handle is like the phosphorus-containing one described above Coating solution but the layer formed therefrom does not cause aging problems and does not have to be washed after their preparation.

According to the invention, this object is achieved by a method in which the body to be provided with an antireflection layer, in wt .-% based on oxide 70-75 SiO ₂ , 8-11 B ₂ O ₃ , 5-9 Al ₂ O ₃ , 7 12 alkali oxides, 0-10 alkaline earth oxides, is wetted with a solution containing, based on the total weight of the solution: 1.0 to 6 Wt .-% HCl 0.5 to 7 Wt.% SiO ₂ sol (solid content) 0.5 to 5 Wt .-% water 85 to 98 % By weight volatile, water-soluble organic solvent

The HCl fraction serves as the acid in a manner known per se for stabilizing the SiO ₂ sol. The SiO ₂ sol (silica sol) can be prepared by known methods, for. Example, by treating an aqueous alkali metal silicate solution with ion exchangers, are prepared. Silica sol is an aqueous solution of colloidal, amorphous SiO ₂ . The commercially available silica sols usually contain from 30 to 60% by weight of SiO ₂ . The average particle diameter is 5 to 150 nm.

The SiO ₂ content in the coating solution is preferably 0.5 to 2.5% by weight. The particle size of the SiO ₂ in the coating solution should be 5 to 50 nm, preferably 8 to 20 nm.

Of the Water content in the coating solution is 0.5 to 5 wt .-%, it comes from usually from the silica sol, the acid and not always anhydrous Solvents.

Of the Remainder of the coating solution consists of a volatile, water-soluble organic solvents. Under volatile it is understood that the solvent a boiling point of 75 to 140 ° C, in particular from 75 to 85 ° C has. As water-soluble solvent are especially polar solvents suitable. Particularly suitable are monohydric lower alcohols with 1 to 5 carbon atoms, z. As methanol, ethanol, propanols, butanols and Pentanols. Furthermore, water-soluble ketones having 3 to 5 carbon atoms are suitable, in particular acetone, methyl ethyl ketone, diethyl ketone. To be favoured Methanol, ethanol, propanols, butanols, dimethyl ketone or mixtures from that.

The Preparation of the solution usually takes place in such a way that the solvent in whole quantity or is submitted to a part, then with stirring the Acid and then stir the silica sol is added and optionally the residual amount of solvent added.

The wetting of the glass body with the coating solution can be done in any way, for. B. by rolling with porous rollers (sponge rollers), by brushing, brushing, flooding, etc., preferably by spraying and more preferably by dipping. During the immersion, the glass bodies to be coated are dipped into the solution (at any speed, provided that only the wheel fluid does not splash and no gas bubbles get caught on the dipping glass body) and pulled out again at a constant speed. Suitable speeds are between 1 ^{mm.s -1} to about 100 ^{mm.s -1} . The aim is to work with the highest possible pulling speed in order to achieve high productivity rates. The rate of drawing depends on the rate of evaporation of the solution and the viscosity of the solution, the conditions of the apparatus, the temperature of the solution and the atmosphere in the drawing area and can be easily optimized by any person skilled in the art with regard to the local conditions. In practice, drawing rates of 1 to 20 mm · s ^-1 have proven successful.

After wetting the glass body with the solution, the layer formed is dried and baked in a conventional manner. The drying can also take place in one step with the baking process, if it is ensured that no gas bubble formation occurs during the evaporation of the solution. The baking is carried out in a conventional manner known to those skilled in the art at temperatures of about 450 ° C (ie below T _g ) up to 35 ° C above the transformation temperature T _{g of} the glass, in particular at temperatures of 575 to 590 ° C. However, baking temperatures above T _{g of} the glass have not yet been used.

The for the Branding needed Time depends on the equipment and can of a Professional easily diagnosed. Usually come burn-in times from about 0.5-1 hour to application.

The produced layer consists of at least 95 wt .-%, preferably at least 99 wt .-% of SiO ₂ . It is particularly preferred if the layer consists entirely of SiO ₂ .

The Layer has a porosity from about 10 to 60% of the layer volume. In this area will be a good antireflection, i. a good passage of light through the anti-reflective glass body reached.

The layer thickness produced by the method is for a good anti-reflection effect between 50 nm and 500 nm. If this layer thickness is not reached, If appropriate, it is preferably another before baking Coating process required, taking before the re-coating process each time the previous coating has to be dried that it does not dissolve in the second coating process. A layer thickness between 80 and 160 nm is preferred.

Of the Pore diameter in the layer produced should preferably 2 to 50 nm, since this pore size is a particularly good antireflexive Effect is achieved.

The method allows, in particular, the production of antireflection coatings on borosilicate glass. The borosilicate glass contains the following constituents (in% by weight based on oxide): SiO ₂ 70-75 B ₂ O ₃ 8-11 Na ₂ O + K ₂ O 7-12 Al ₂ O ₃ 5-9 alkaline earth oxides 0-10

On Borosilicate glass with a different glass composition increases the adhesive and wipe resistance of the coating significantly.

Especially suitable are glasses of the composition 70-75 SiO ₂ , 8-11 B ₂ O ₃ , 6-8 Al ₂ O ₃ , 6-8 Na ₂ O, 1-4 K ₂ O, 7-12 Σ alkali oxides, 0- 2 CaO.

One special cleaning step before wetting, z. B. by spray coating or dipping the vitreous body in the coating solution is not usually required. Only if the glass body during the Transport or storage must be contaminated Pollutions are removed by a washing process again.

The Coating is particularly suitable for coating borosilicate glass bodies of above-mentioned compositions as a glass tube, glass rod or glass plate, for producing a device in solar thermal, especially during domestic water heating, Process heat and especially in parabolic trough power plant technology.

With According to the invention, antireflection coatings can be applied to borosilicate glass which are resistant to aging without further notice and over one excellent wiping resistance feature.

Examples

1. Preparation of the coating solutions

• A) Prior art (phosphate-containing) Analogous to US 6,998,177 B2 In Example 1, a coating solution was prepared as follows: 235.8 g of isopropanol was mixed with 206.0 g of 1 N-HNO ₃ and stirred for 10 minutes. Then, 44.5 g of 85% H ₃ PO _{4 was} added and stirred again for 5 minutes. Thereafter, 271.2 g of silica sol (Köstrosol 0830A, 30% SiO ₂ , manufacturer Chemiewerke Bad Köstriz) was added and stirred for a further 5 minutes. This mixture was diluted with 3301 g of isopropanol and then allowed to stand for one day. After that, the solution was ready to use.
• B) State of the art (phosphate-free) Analogous to US 6,998,177 B2 In Example 2, a phosphate-free coating solution was produced as follows: According to procedure A), a corresponding solution was produced with the following changes: no phosphoric acid was added, 268.8 g of silica sol were used.
• C) According to the Invention A coating solution according to the invention was produced as follows: 2165 g of 5N-HCl were added to 235.8 g of isopropanol, the solution was stirred for 1 minute, then were added 268.8 g of silica sol (Köstrosol 0830A), it was again stirred for 1 minute, the mixture was treated with 3301 g of isopropanol and stirred for 5 minutes. After that, the solution was ready to use.

2. Coating process

Glass tubes of the composition (in% by weight based on oxide) 73 SiO ₂ , 9.5 B ₂ O ₃ , 7 Al ₂ O ₃ , 7 Na ₂ O, 3 K ₂ O and 0.5 CaO (glass no. 1) with an outer diameter of 125 mm and a wall thickness of 3 mm and a length of 500 mm were immersed along their longitudinal axis 250 mm deep in the coating solution. The immersion speed was 10 mm · s ^-1 . After a residence time of about 10 seconds, the glass tube was pulled out of the coating solution at a speed of 3.8 ^{mm.s -1} . The drawing process formed a wet film on the glass. The coated glass was either in a heated chamber at a temperature of 575 ° C, ie 10 ° C above T _{g of} the glass, treated for 1 hour or at 500 ° C, ie 65 ° C below T _{g of} the glass, for 1 hour treated.

For comparison, a glass tube of a borosilicate glass of the composition (in% by weight based on oxide) of 81 SiO ₂ , 13 B ₂ O ₃ , 2 Al ₂ O ₃ , 3.5 Na ₂ O and 0.5 K ₂ O was coated (Glass No. 2). The glass tube had an outer diameter of 100 mm and a wall thickness of 2.5 mm

3. aging resistance

The coated tubes were stored in open air for up to 9 months. It was checked whether visually clouding or fading of the color of the antireflection layer occurred.

4. Wipe test

There the wipe test according to DIN 58196 5 only suitable for flat glass samples is, he was for examination The coated tubes modified accordingly.

The wiper body is a standardized eraser with the specification MILE-12397. The glass tube was clamped and the eraser was reciprocated over the coating with a 1 kg contact surface by means of a movable carriage along the tube axis at a speed of 10 mm.s ^-1 . The number of swipe strokes up to complete layer removal is a measure of the smudge resistance of the layer. The wipe test was performed immediately after baking the coating ("at the beginning") and repeated after some time.

5. Results

The results are summarized in Table 1. Table 1 Glass no. Stoving temperature [° C] aging resistance Wipe test [strokes] Example 1 with phosphate (solution A) (prior art) 1 500 strongly faded after 3 weeks (almost colorless) initially> 50 after 3 months aging> 50 1 575 strongly faded after 3 weeks, stronger than at burning temp. 500 ° C initially> 50 after 3 months aging> 50 Example 2 Phosphate-free (solution B) (prior art) 1 500 severely faded after 3 weeks, dot-like cloudiness after 3 weeks, very cloudy after 3 months initially 36 after 3 weeks aging 2 1 575 strongly faded after 3 weeks, very cloudy after 3 weeks initially 36 after 3 weeks aging 2 Example 3 Solution C according to the invention 1 500 no fading or clouding initially> 50 after 9 months aging> 50 1 575 no fading or clouding initially> 50 after 9 months aging> 50 Example 4 Solution A 2 500 no fading, but crystal-like efflorescence, recurring even after washing initially 50 after 10 days aging 10 Example 5 Solution C 2 as example 4 initially 50 after 10 days 15

Out these examples become superiority the method according to the invention clear.

Claims (7)

A method for producing an adhesion and smear-resistant, porous SiO ₂ -containing antireflection layer on a borosilicate glass body characterized by the following steps - wetting the body to be coated, which contains (in wt .-% based on oxide) 70-75 SiO ₂ 8-11 B ₂ O ₃ 5-9 Al ₂ O ₃ 7-12 alkali 0-10 alkaline earth oxides with a coating solution - which contains 1.0 to 6.0 Wt .-% HCl 0.5 to 7.0 Wt.% SiO ₂ sol (solid content) 0.5 to 5 Wt .-% water 85 to 98 % By weight volatile, water-soluble organic solvent, and - Drying and baking of the coating. A method according to claim 1, characterized by using a coating solution 1.0 to 6.0 Wt .-% HCl 0.5 to 7.0 Wt.% SiO ₂ sol (solid content) 0.5 to 5.0 Wt .-% water 85 to 98 Wt .-% methanol and / or ethanol and / or propanol and / or butanol and / or Dimethyl ketone and / or methyl ethyl ketone. Method according to claim 1 or 2, characterized that the wetting of the body to be coated by immersion in the coating solution he follows. A method according to claim 3, characterized in that the removal from the dipping solution at a rate of 1 to 100 mm · s ^-1 , in particular 1 to 20 mm · s ^-1 occurs. A method according to claim 1 or 2, characterized in that the borosilicate glass body contains (in wt .-% based on oxide): 70-75 SiO ₂ 8-11 B ₂ O ₃ 6-8 Al ₂ O ₃ 6-8 Na ₂ O 1-4 K ₂ O 7-12 Σ alkali oxides 0-2 CaO Coating solution for producing an antireflection coating on borosilicate glass containing 1.0 to 6.0 Wt .-% HCl 0.5 to 7.0 Wt.% SiO ₂ sol (solid content) 0.5 to 5 Wt .-% water 85 to 98 % By weight volatile, water-soluble organic solvent Coating solution according to claim 5, characterized by a content of 1.0 to 6.0 Wt .-% HCl 0.5 to 7.0 Wt.% SiO ₂ sol (solid content) 0.5 to 5 Wt .-% water 85 to 95 Wt .-% methanol and / or ethanol and / or propanol and / or butanol and / or Dimethyl ketone and / or methyl ethyl ketone.